1. Field of the Invention
The present general inventive concept relates to an image forming apparatus. More particularly, the present general inventive concept relates to an image forming apparatus that determines a transfer voltage or a transfer current.
2. Description of the Related Art
A conventional image forming apparatus forms an image for outputting contents generated by a computer program on a recording medium. Particularly, the conventional image forming apparatus forms an electrostatic latent image by scanning light to a photosensitive medium, develops the electrostatic latent image with a developer, and transfers and fixes the developed electrostatic latent image on a paper so as to form an image.
FIG. 1 illustrates a transfer process of a conventional image forming apparatus. As illustrated in FIG. 1, the conventional image forming apparatus sets a transferring unit 2a disposed closest to an attraction unit 1, which uses an attraction roller 1a, as a reference transferring unit among a plurality of transferring units 2, and obtains a resistance value of the transferring unit 2a by detecting a current flowing to the transferring unit 2a so as to determine an optimal transfer voltage and/or current in a pre-printing process which is performed before printing on a recording medium. Herein, a resistance value of the transferring unit 2a is obtained by using a photosensitive material, a conveyer belt that passes the corresponding transferring unit 2a, and a transfer roller that is disposed facing the photosensitive material with respect to the conveyer belt and transfers a toner that has been developed to a charged photosensitive material to the recording medium.
Therefore, when the resistance value of the transferring unit 2a is obtained, the conventional image forming apparatus detects a current flowing to the attraction unit 1 and obtains a resistance value thereof. In this case, the resistance value of the attraction unit 1 is determined by the attraction roller (ATTR) 1a that attracts the recording medium to the conveyor belt and a driving roller that moves the recording medium to be transferred to the transferring unit 2 by the conveyer belt.
When the recording medium enters into the attraction unit 1, the conventional image forming apparatus obtains the resistance value of the attraction unit 1 by detecting the current flowing thereto so as to obtain a resistance value corresponding to the recording medium.
An optimal transfer voltage for a transferring operation can be determined by the resistance value obtained in such a manner.
However, the conventional image forming apparatus obtains the resistance value of the transferring unit 2a located closest to the attraction unit 1. Therefore, when power is applied to the attraction unit 1 for obtaining the resistance value of the attraction unit 1, a leakage current from the attraction unit 1 interacts between the transferring unit 2a and the attraction unit 1, and it is difficult to obtain the accurate resistance value of the transferring unit 2a. 
FIG. 2 illustrates a transferring process of the conventional image forming apparatus for a recording medium with respect to time.
As illustrated in FIG. 2, the conventional image forming apparatus obtains the resistance value of the transferring unit 2a during time t1 to time t2, and then obtains the resistance value of the attraction unit 1 during time t2 to time t3 after perception of the resistance value of the transferring unit 2a is completed.
Then, at a time after passing time t4 to time t5 but before the recording medium enters into the attraction unit 1, the conventional image forming apparatus obtains a resistance value of the recording medium entering the attraction unit 1 during time t5 to time t6. Through the obtained resistance value, the transfer process is performed on the recording medium after time t6.
In this case, since the leakage current from the attraction unit 1 interacts between the attraction unit 1 and the transferring unit 2a, the resistance value of the transferring unit 2a and the resistance value of the attraction unit 1 cannot be simultaneously obtained, but has to be separately obtained during time t1 to time t2 and time t2 to time t4, thereby increasing a pre-printing time for printing the recording medium.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present general inventive concept, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.